Box jellyfish may seem like rather simple creatures, but in fact their visual system is anything but. They've got no fewer than 24 eyes of four different kinds. Now, researchers reporting online on April 28 in Current Biology, a Cell Press publication, have evidence revealing that four of those eyes always peer up out of the water, regardless of the way the rest of the animal is oriented. What's more, it appears that those eyes allow the jellies to navigate their way around the mangrove swamps in which they live.
"It is a surprise that a jellyfishan animal normally considered to be lacking both brain and advanced behavioris able to perform visually guided navigation, which is not a trivial behavioral task," said Anders Garm of the University of Copenhagen. "This shows that the behavioral abilities of simple animals, like jellyfish, may be underestimated."
In fact, scientists have known for more than a century that box jellyfish had a unique array of eyes. It was known that they could rely on vision to respond to light, avoid obstacles, and control their rate of swimming. But box jellyfish generally live in shallow waters with plenty of obstacles. The species Garm's team studied, Tripedalia cystophora, lives between the prop roots in Caribbean mangrove swamps, where they stay close to the surface to catch and eat copepods that gather in high densities in light shafts formed by openings in the mangrove canopy. They are never found out in the open, where they might risk starvation. That means they must stay within a rather restricted area, less than two meters wide. And it now appears that they have eyes that help them do this.
The researchers examined the function of one of two types of "upper lens eyes," already known to form images, to work out just what those eyes can see and how well. It turns out that those four eyes cover precisely the visual field needed to see through the water's surface up into the world above. The resea
|Contact: Elisabeth Lyons|